Designing and building small molecules for the purpose of function enables advancement in fields ranging from pharmaceuticals to pesticides. The Diels-Alder (DA) reaction is one of the most powerful and robust transformations for assembling cyclic molecular frameworks, employing a plethora of diene (4π) and dienophile (2π) components capable of delivering a rich diversity of cyclic compounds poised for function. One structural variant is the dehydro-Diels-Alder (DDA) reaction, where one, two, or all three of the double bonds of the classic diene and dienophile are replaced with triple bonds, providing access to substituted aromatic compounds not accessible using other chemistries. The energy price to incorporate the high degree of precursor unsaturation required for the formation of aromatic products can be mitigated by the propensity of cyclohexadiene derivatives to aromatize. Aromatic derivatives, in turn, can be prepared from more saturated precursors, a process defined as a dehydrogenative DA reaction.
A particularly problematic, but potentially useful dehydrogenative DA reaction involves the use of styrene as the diene component and an alkyne dienophile, affording a cycloadduct that can aromatize under oxidative conditions to give naphthalene derivatives (Scheme 1). Problems that can arise when using styrene as the diene range from polymerizations to [2+2] cycloaddition reactions. One solution is to use very reactive dienophiles such as maleic anhydride or benzoquinone. However, the desired cycloadducts are typically obtained in low yields because the reactivity of these dienophiles leads to a second DA reaction with the newly formed diene of the first cycloadduct. Lack of regioselectivity for the styrenyl DA reaction is also a drawback, which can be overcome by carrying out the reaction intramolecularly. The intramolecular styrenyl DA reaction also suffers from low yields and long reaction times, producing mixtures of inseparable dihydronaphthalene and naphthalene products.

Continued interest in the development of an efficient styrenyl DA reaction is driven by the need for functionalized naphthalene compounds that can serve as valuable building blocks for the synthesis of small molecules in many important areas, such as pharmaceuticals, chiral reagents, liquid crystals, and organic dyes. Moreover, the intramolecular styrenyl DA reaction affords a unique functionalization pattern on the resulting naphthalene derivatives that complements other synthetic approaches.
Fluorescent-based tools are widely used to monitor environments of biological events. Small organic fluorophores are particularly powerful due to rapid response times for monitoring real-time events with excellent spatial resolution. Moreover, their relatively small size minimizes disruption of the environment being studied. Thus, new small molecule-based chemical sensors are continually being developed. Many of these developments involve modifying an existing fluorophore to accommodate a need. For example, Prodan is a compound whose fluorescent emission and quantum yield is unusually dependent upon solvent polarity; in cyclohexane the fluorescent emission is 410 nm and in water it is 534 nm, a bathochromic shift of 124 nm. Prodan is considered to be state of the art for application in biological systems and structural variants of this probe have been prepared, such as the lipophilic Laurdan; the thiol reactive Acrylodan and Badan; and the amino acid-containing Aladan. In addition, a spectrally red-shifted compound, Anthradan, has been prepared that incorporates an anthracene ring between the electron donating and electron withdrawing groups; the emission spectra in hexanes is 483 nm, and in methanol 604 nm. The design and synthesis of new naphthalene-containing fluorophores could be significantly enhanced by novel methods for the construction of aromatic rings.